Exposure to genotoxic agents is generally believed to result in a range of biological effects including cancer. In the last 10 years there has been an intensive effort in the development of analytical methods to assess human exposure to potentially genotoxic agents. In our studies we have employed 32P-postlabeling to investigate the formation of DNA adducts. The results of these studies have established that DNA adduct formation can be used as a molecular dosimeter for occupational exposure to agents such as benzene and styrene. In addition we have applied postlabeling to investigate DNA adduct formation by the anti-estrogenic agent tamoxifen. Our studies have established that tamoxifen can be metabolized to reactive intermediates that form DNA adducts. In conjunction with the mass spectrometry facility, we are in the process of identifying the structures of the DNA adducts detected by 32P-postlabeling. Without access to these facilities we would be unable to identify these DNA adduct structures.